Some havoc adolescents cause with fruit (7)
I believe the answer is:
avocado
'fruit' is the definition.
(I know that avocado is a type of fruit)
'some havoc adolescents cause' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'AVOCADO' is hidden in the letters of 'havoc adolescents cause'.
'with' acts as a link.
(Other definitions for avocado that I've seen before include "Savoury pear-shaped fruit" , "Yellowish green" , "Fruity type" , "Dark green pear-shaped fruit" , "Evergreen" .)